The semiconductor industry currently produces different types of semiconductor-based image sensors that use micro-lenses, such as charge coupled devices (CCDs), CMOS active pixel sensors (APS), photodiode arrays, charge injection devices and hybrid focal plane arrays, among others. These image sensors use micro-lenses to focus electromagnetic radiation onto photo-conversion devices, e.g., photodiodes. Also, these image sensors can use color filters to pass particular wavelengths of electromagnetic radiation for sensing by the photo-conversion devices, such that the photo-conversion devices typically are associated with a particular color.
Micro-lenses help increase optical efficiency and reduce crosstalk between pixel cells of an image sensor. FIGS. 1A and 1B show a top view and a simplified cross section of a portion of a conventional color image sensor using a Bayer color filter patterned array 100 (described below). The array 100 includes pixel cells 10, each being formed on a substrate 1. Each pixel cell 10 includes a photo-conversion device 12r, 12g, 12b, for example, a photodiode, and a charge collecting well 13r, 13g, 13b. The illustrated array 100 has micro-lenses 20 that collect and focus light on the photo-conversion devices 12r, 12g, 12b, which in turn convert the focused light into electrons that are stored in the respective charge collecting wells 13r, 13g, 13b. 
The array 100 can also include or be covered by a color filter array 30. The color filter array 30 includes color filters 31r, 31g, 31b, each disposed over a pixel cell 10. Each of the filters 31r, 31g, 31b allows only particular wavelengths of light to pass through to a respective photo-conversion device. Typically, the color filter array is arranged in a repeating Bayer pattern that includes two green color filters 31g for every red color filter 31r and blue color filter 31b, arranged as shown in FIG. 1A.
Between the color filter array 30 and the pixel cells 10 is an interlayer dielectric (ILD) region 3. The ILD region 3 typically includes multiple layers of interlayer dielectrics and conductors that form connections between devices of the pixel cells 10 and from the pixel cells 10 to circuitry 150 peripheral to the array 100. A dielectric layer 5 is typically provided between the color filter array 30 and microlenses 20.
One major disadvantage of the Bayer pattern color filter, and of other color filter patterns that use alternating RGB filters over a single array, is that crosstalk among the pixels can effectively reduce color reconstruction capabilities. Crosstalk can occur in two ways. Optical crosstalk occurs from several sources, on being when light enters the microlens at a wide angle and is not properly focused on the correct pixel. An example of angular optical crosstalk is shown in FIG. 1B. Most of the filtered red light 15 reaches the correct photo-conversion device 12r, but some of the filtered red light 16 intended for red photo-conversion device 12r is misdirected to adjacent green and blue pixels.
Electrical crosstalk can also occur in the array through a blooming effect. Blooming occurs when the intensity of a light source is so intense that the charge collecting well 13r, 13g of the pixel cell 10 cannot store any more electrons and provides extra electrons 17 into the substrate and adjacent charge collecting wells. Where a particular color, e.g., red, is particularly intense, this blooming effect can artificially increase the response of adjacent green and blue pixels.
It would, therefore, be advantageous to have alternative color filter arrangements for use in an image sensor to provide more accurate color data and which mitigates against optical and electrical crosstalk.